Pacing lead for a left cavity of the heart, implanted in the coronary system

ABSTRACT

A pacing lead for a left cavity of the heart, implanted in the coronary system. This lead ( 24 ) includes a lead body with a hollow sheath ( 26, 28 ) of deformable material, having a central lumen open at both ends, and at least one telescopic microcable ( 42 ) of conductive material. The microcable slides along the length of the lead body and extends beyond the distal end ( 32 ) thereof. The party emerging beyond the distal end is an active free part ( 34 ) comprising a plurality of distinct bare areas ( 36, 38, 50, 50′, 50″ ), intended to come into contact ( 40 ) with the wall of a target vein ( 22 ) of the coronary system ( 14 - 22 ), so as to form a network of stimulation electrodes electrically connected together in parallel. The microcable further comprises, proximally, a connector to a generator of active implantable medical device such as a pacemaker or a resynchronizer.

RELATED APPLICATIONS

The present application claims the benefit of French Application No.10/59521 entitled “Pacing lead for a left cavity of the heart, implantedin the coronary system” and filed Nov. 19, 2010, which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to “active implantable medical devices” asdefined by the 20 Jun. 1990 Directive 90/385/EEC of the Council of theEuropean Communities, more particularly to devices that continuouslymonitor a patient's heart rhythm and deliver to the heart, if necessary,electrical pulses for stimulation, resynchronization, cardioversionand/or defibrillation, and even more particularly to cardiac pacingleads intended to be implanted in the coronary network of the heart forstimulation of a left ventricular or atrial cavity.

BACKGROUND

For the right cavities of a patient's heart, it is generally sufficientto implant endocardial leads through the right peripheral venousnetwork. The implantation of permanent leads in a left heart cavity,however, involves significant operational risks, for example, thepassage of bubbles to the vascular network of the brain locateddownstream of the left ventricle. For this reason, when the left cavityhas to be stimulated, most often a lead is not introduced not the cavityto be stimulated, but rather into the coronary system, with the leadhaving an electrode that is guided to the left ventricle or left atriumand applied against the wall of the epicardium, as appropriate.

A lead of this type is, for example, the Situs LV model, marketed bySorin CRM S.A.S. (Clamart, France) and described in EP 0993840 A1 andits US counterpart U.S. Pat. No. 6,385,492 (both assigned to Sorin CRMS.A.S., previously known as ELA Medical). Such a lead is introducedthrough the coronary sinus opening into the right atrium, by anendocardial approach. The lead is then guided and pushed along thecoronary vein network to the chosen stimulation site. This interventionis very difficult, given the peculiarities of the venous network and itsaccess paths, including the passage through valves and tortuosities, aswell as experiencing a gradual reduction in diameter of the vein as thelead is advanced along the selected coronary vein. Once the target veinis reached, the surgeon must then, first of all, ensure the mechanicalstability of the lead into the vein.

Another problem is the difficulty of finding a good stimulation site, toobtain good electrical contact between the stimulating electrode and thetissue of the epicardium, and maintain this contact over time.

In addition, the surgeon must ensure that the chosen stimulation pointdoes not generate phrenic nerve stimulation.

To overcome these difficulties, it was proposed to have multipleelectrodes along the lead body to increase the chances of an acceptablecompromise, by possibly giving the lead body a particular conformation.The surgeon can choose from among the various electrodes present on thelead body to find the one that provides the best efficiency from theelectrical and hemodynamic points of view. One such multiple electrodelead is described in EP 1938861 A1 and its US counterpart US PatentPublication No. 2008/0177343 (both assigned to Sorin CRM S.A.Spreviously known as ELA Medical). These leads allow in particular toimplement the concept of “electronic repositioning” to direct orredirect the electrical field between different electrodes arrangedalong the pacing lead of the left cavity and/or with an electrode of thepacing lead of the right cavity. The technology allows managing themicro-movements or changes in the hemodynamic behaviour (reversemodeling) simply by reprogramming the generator via telemetry throughthe skin, without major surgery.

The counterpart of this solution is an increasing complexity of thestructure of the lead, an increase of the number of electrodes causingan increase in the number of components, and therefore of electricalconnections, or the use of multiplexing circuits for selecting thevarious electrodes present on a same lead.

US Patent Publication No. 2009/157136 A1 describes a technique ofsearching for an optimal pacing site using a temporary mapping catheterto be introduced into the coronary sinus. This catheter is a flexibletube open at both ends, and has, optionally, a guide wire. It isequipped with electrically independent multiple distal electrodes, andat its proximal side, a connector for connection to a data acquisitionsystem for identifying the best stimulation site with an algorithm basedon cardiac motion.

A permanent conventional multi-electrode lead, having for example astandard diameter of 4.5 to 6 French, is then placed at the selectedlocation, using either the guide wire and a standard over the wire(“OTW”) technique, or the tube, of the temporary catheter.

Another recent development for a left ventricle pacing lead is to reducethe diameter of the implantable part in the coronary system, to adiameter of 4 French (1.33 mm).

The size of the lead body is indeed a factor directly related to thecapacity of controlled guiding of the lead in the coronary venoussystem, so as to select particular stimulation sites located in somespecific collateral veins. These sites are reached by means of a veinsub-selection catheter used to place a guiding stylet at the chosensite. Once the vein is selected and the stylet is placed, the surgeonadvances the lead body which slides on the stylet, the latter acting asa guide wire of small diameter axially guiding the lead body to thechosen location (an OTW technique).

These solutions however have two notable limitations: (1) The finenessof the lead, whose diameter does not allow to access the deepestcollateral veins: for example, the Situs lead referenced above has adiameter of 2.2 mm (6.6 French) and requires a 7 French diameterintroducer, and (2) The correct positioning and good maintaining of theelectrical contact of the electrode against the tissue to causestimulation.

The above techniques of multi-electrode leads and electronicrepositioning make possible to (more or less appropriately) overcome thesecond limitation, however they increase the first limitation, to theextent that the multiplication of electrodes and of the internalconductors or components necessarily implies an increase in the diameterof the lead body which reduces its flexibility, making it difficult oreven impossible to ensure passage through the tortuous coronary venoussystem.

The solutions heretofore known are therefore always a compromise betweenthese two constraints.

OBJECT AND SUMMARY

It is, therefore, an object of the invention to provide a left heartcavity pacing lead having a very small diameter and an active part forstimulating multiple areas of the epicardium.

It is another object of the invention to propose such a lead having asimple structure that is inexpensive to manufacture, reliable, andavoids problems related to the design and use of multiple electrodeleads.

Broadly, the present invention provides a coronary sinus lead that, oncethe site of stimulation is selected and assessed, ensures optimum andsustainable stability of the stimulating electrode on this site.

The present invention also allows separating the problem of thestability from that of the electro-hemodynamic performance. Indeed, asit will be seen, the stability is ensured by the distal end of the lead(having a predefined shape such as a screw made of silicone), while thestimulation is provided by a telescopic microcable equipped with one ormore continuous or disjointed pacing areas.

In particular, if it can be ensured that the electrode remains in place,regardless of at what site or place it was originally implanted, furthermovements of the lead are prevented, stability is achieved, and it is nolonger necessary to overcome the consequences of such a displacement bycomplex techniques, such as electronic repositioning or the selectionamong multiple electrodes.

Essentially, one embodiment of the invention is for a pacing lead,intended to be implanted in a coronary network vein for the stimulationof a left cavity of the heart, including the elements known from the USPatent Publication No. 2009/157136 A1 cited above, that is to saycomprising a telescopic microcable in a conductive material, comprisingat its distal end an active free part comprising a plurality of distinctbare areas, these bare areas being intended to come into contact withthe wall of a target vein of the coronary network, so as to form anetwork of stimulation electrodes. The cable further comprises, on itsproximal side, means for coupling the network of stimulation electrodesto a generator of an active implantable medical device, such as apacemaker or a resynchronizer. Such a coupling means may be, forexample, a terminal that can be inserted into a standard connector headof the implantable device, or is otherwise electronically connected,directly or indirectly, to a pulse generator output of an implantedaction medical device.

In a preferred embodiment, the cable is a telescopic microcable thediameter of which is between 0.5 and 2 French, made of a plurality ofmicrowires twisted together, in which at least some of the plurality ofstrands incorporate either a core having a radiopaque material, such asplatinum-iridium or tantalum wrapped in a sheath of mechanically durablematerial such as NiTi or stainless steel, or vice versa. In addition,the distinct bare areas are preferably bare areas of the microcable, andform a network of stimulation electrodes electrically connectedtogether.

The small diameter microcable (more typically from 1 to 2 French) isadvantageously used to catheterize veins of very small diameter, whichhave not before been exploited due to the larger size of the previouslyknown permanent coronary probes.

The dual constraint mentioned above is thus overcome by the microcablestructure, which in a preferred embodiment, is a structure without aninternal lumen, and with several microwires twisted together, aconfiguration capable of both ensuring endurance against cardiacmovements and resistance to the stresses during implantation.

This microcable is suitable to be introduced into the coronary networkvia a permanent carrier lead (e.g., with no particular mappingcapacity), previously placed into the vein.

The small diameter is the essential characteristic that divides thesurface of the monopolar electrode through multiple windows arrangedalong the body of the microcable. This allows permanent stimulation of alarge area of the heart wall via this monopolar microlead. For diametersof between 1 and 2 French, it would not be possible to provide anindividual isolation of each strand that can withstand the abrasionconstraints between strands.

Various embodiments can be envisaged.

In one embodiment, the present invention provides a pacing lead,intended to be implanted in a coronary network vein for the stimulationof a left cavity of the heart, comprising a telescopic microcable madeof a conductive material, having at its distal end an active free partcomprising a plurality of distinct bare areas. These distinct bare areasare intended to come into contact with the wall of a target vein of thecoronary network, so as to form a network of stimulation electrodeselectrically connected together. The microcable further comprises, atits proximal end, means for coupling to a generator of an activeimplantable medical device, such as a pacemaker or a resynchronizer.

Preferably, the distal end of the microcable comprises a two-orthree-dimensional pre-formed shape, having external dimensions in a reststate that are typically included within a cube having dimensions ofbetween 1 to 90 mm per side. The microcable can thus be implanted alone,and held in place by its own particular distal pre-formed shape. In thisembodiment, the placement in the vein is carried out by conventionalmeans such as catheter/sub-catheter or brain access catheter.

Another embodiment of the present invention is directed to a systemcomprising a microcable and a lead body having a hollow sheath made of adeformable material, a central lumen open at both ends and in which themicrocable is positioned, ready to slide by extending along the entirelength of the lead body and beyond its distal end, such that the part ofthe microcable emerging beyond the distal end of the lead body is theactive free part of the microcable.

To ensure maintaining the position of the microcable in the vein, thedistal end of the lead body may be provided with a retaining means,including at least one relief formed on the lead body. Preferably, theat least one relief includes an helical relief with a thread wrappingaround the lead body, having a locally increased diameter compared tothat of the lead body itself, including a diameter greater than or equalto 7 French.

The lead body preferably includes a main part distally extended by atransition portion having a smaller diameter than that of the main part,including a diameter of the main part lower or equal to 6 French and adiameter of the transition part less than or equal to 5 French.

In yet another embodiment, the lead comprises a common lead body and aplurality of separate telescopic microcables, each of which is housed inthe lead body and is slidable therein, the respective active free partsof the different microcables emerging from the lead body in separatelocations, longitudinally spaced along the lead body. Preferably, in allcases, the diameter of each microcable is typically between 0.5 and 2French, with an exposed total surface of the distinct bare region(s) ofthe active free part of the microcable of at least 1 mm², morepreferably between 4 and 6 mm² and a length of the active free partbeing adjustable between 1 and 200 mm.

In one embodiment, the active free part of the microcable comprises aplurality of distinct bare regions that successively extend along theactive free part of the microcable. More preferably, these distinct bareareas are separated from each other by portions of tube made of anelectrically non-conductive material, wrapping and sheathing themicrocable between two consecutive bare areas. The bare areas also maybear tubular rings made of an electrically conductive material, whichare crimped on the microcable. The electrically conductive material ofthe tubular rings inserted on the microcable is preferably made of aradio-opaque material.

In another embodiment, the microcable includes a stranded structurecoated with an insulating material, including parylene, in which thedistinct bare areas are formed by ablation forming openings in theinsulating material along the microcable. Preferably, titanium nitrideis then deposited on the distinct bare areas thus formed.

Preferably, the length in the longitudinal direction of each bare areais typically selected to be between 0.5 and 10 mm.

The microcable is advantageously formed of a plurality of strandstwisted together, in which at least some strands incorporating either acore made of a radiopaque material, such as platinum-iridium, wrapped ina sheath of a mechanically durable material such as NiTi or stainlesssteel, or vice versa.

In another embodiment of the invention, the active free part of themicrocable has at least an helically bare area extending along theactive free part. The microcable can notably include, on at least oneportion of the active free part, a strand formed of a plurality oftwisted strands having a surface with a corresponding plurality ofhelical bare regions, isolated from each other in the circumferentialdirection by helical coatings of an electrically non-conductivematerial.

Advantageously, a lead in accordance with the present invention has avery small diameter, able to exploit the entire length of the vein andmake an optimal use of all the veins present in the basal zone,especially to avoid the risk of phrenic nerve stimulation, whichgenerally increases when the lead is too distal. In addition, the leftheart pacing lead ensures an excellent and durable electrical contactwith the tissues to be stimulated. A further advantage of the lead isthat it increases or expands the areas of stimulation, allowing (asopposed to traditional leads) stimulation of multiple areas of theepicardium, thereby improving the chances of an optimalresynchronization.

DRAWINGS

Further features, characteristics, and advantages of the presentinvention will become apparent to a person of ordinary skill in the artfrom the following detailed description of preferred embodiments of thepresent invention, made with reference to the annexed drawings, inwhich:

FIG. 1 shows the heart and its coronary venous network in which a leadaccording to the invention is implanted;

FIG. 2 illustrates an active part of a microcable of a first embodimentof the lead of the present invention;

FIG. 3 is an enlarged view of the detail marked III in FIG. 2;

FIG. 4 is an enlarged view of an active part of the lead of a secondembodiment of the invention;

FIG. 5 is a graph representing a method to adjust the exposed activearea by an appropriate selection of the diameter of the insulationcoating on the active part of the lead illustrated in FIG. 4; and

FIG. 6 illustrates a third embodiment of the invention, wherein the leadcarries a plurality of separate microcables.

DETAILED DESCRIPTION

With reference to the drawings, FIGS. 1-6, preferred embodiments of adevice in accordance with the present invention will now be described.

FIG. 1 generally illustrates the myocardium, in which a lead 26 forpacing of the left ventricle according to the present invention has beenintroduced. Lead 26 is endocardially implanted in the venous coronarynetwork via the superior vena cava 10, the right atrium 12 and the entry14 of the venous coronary sinus. The venous coronary system thendevelops into several branches, including the postero-lateral vein 16,the lateral vein 18, the great cardiac vein 20 and the antero-lateralvein 22.

Reference 24 generally designates the lead of the invention, whichincludes a lead body having a main part 26 (e.g., a 6 French diameter)entering into the coronary sinus 14, extended by a transition portion 28of the same conformation but of smaller diameter (e.g. 4.8 French) toallow better penetration into the coronary venous system.

This lead body is formed of a tubular hollow sheath made of a deformablematerial, such as silicone or polyurethane, defining a central lumenextending from one end to the other of lead body.

At the distal end, the lead body is provided with retaining means 30 toallow its mechanical support in the vein. This retaining means may be,for example, a screw as described in EP 1374945 A1 and its counterpartU.S. Pat. No. 7,483,753 (both assigned to Sorin CRM S.A.S. previouslyknown as ELA Medical), equipped with a helical thread having a maximumouter diameter of about 7 French. See FIG. 6. This retaining means is ofthe same type as that used by the aforementioned Situs LV model lead.The screw thread is molded in a cylindrical element terminating thetransition part 28 of the lead body, the whole assembly preferably beingmolded in one piece in a material such as a silicone rubber, or asimilar material that is not traumatic and ensures goodbiocompatibility. Moreover, the distal end of the lead body, providedwith the retaining means 30 is open at lumen end 32, the outletincluding a sealing means (not shown, but of a conventional design), forexample, a penetrable silicone plug to prevent any backflow of bloodinside the lead body in both the absence and the presence of an elementintroduced into the central lumen of the lead body.

This lead body is implanted according to a conventional OTW technique byuse of a very thin stylet forming a guide wire, provided at its distalend with a flexible end for not being traumatic and for allowing itsdirect introduction into the vessels of the coronary system without riskof perforation. Previously, the surgeon has a main catheter allowing himto access at the end of the coronary sinus and a sub-selection catheterto choose, under fluoroscopy, the path of the venous system that allowsachieving the target vein corresponding to the chosen stimulation site.

The surgeon then introduces the guide wire into the catheter, and pushesit to advance it in the coronary venous system in order to select aparticular collateral vein. Once the collateral vein is selected, thesurgeon pulls on the guide wire for the lead body (the guide wire passesthrough the orifice 32 which is normally closed by the penetrable plug).He then drags and moves the lead body on the guide wire, which axiallyguides the lead body to the chosen location. Once the lead body is atthe final position in the chosen vein, the surgeon gives the lead bodyan additional motion of rotation, which ensures, by screwing the threadof the retaining means 30, the further progression of the lead body of afew millimetres with a corresponding reinforcement of the anchoring ofthe lead body into the vein.

Typically, the lead body as described above (having a well-known andconventional structure) is extended by a telescoping microcablepresenting the active part 34 of the lead (possibly in addition to apre-existing active stimulation electrode, arranged on the lead).Preferably, the microcable has a diameter of about 0.5 to 2 French andextends over a length of 1 to 200 mm beyond the outlet 32 of the distalend of the lead body.

Once the lead body is implanted by the method indicated above and afterremoval of the guidewire, the microcable is then inserted into the leadbody at its proximal end. It is pushed along the length of the lead bodyto emerge from the outlet 32, then is deployed beyond the outlet 32 soas to advance, under fluoroscopy in the collateral veins up to thedesired position. It is thus possible to reach and stimulate areas ofthe coronary venous system previously inaccessible with the prior knownleads.

The active part 34 of the microcable (i.e., its emerging part) has aplurality of distinct bare parts forming a succession of individualelectrodes, together constituting an array of electrodes connected inseries forming multiple stimulation points. For example, in FIG. 2,active part 34 includes, in addition to the distal electrode 36, aplurality of ring electrodes 38 arranged at regular intervals along thelength of the active portion 34. This allows more opportunities forpoints 40 to make contact with the wall of the vein and thus to ensure amulti-zone distribution of the stimulation energy at several points ofthe epicardium and therefore of the left ventricle.

FIGS. 2 and 3 illustrate a first embodiment of an active part (the onelinked to the emerging part of microcable) of the lead of the invention.The core of active portion 34 is formed by microcable 42, on whichinsulating tubes 44 and short conducting electrodes 38 are successivelyand alternately threaded. Microcable 42 is terminated by distalelectrode 36. The microcable 42 is advantageously made of a nitinol(NiTi alloy) core, a material whose main advantage is its extremefatigue endurance. Preferably, the microcable structure has a pluralityof strands in which each strand consists of a core of platinum-iridiumcoated with a thickness of nitinol (or vice versa). The system is thenpossibly coated either by a thin layer of parylene (e.g., of C type), orby a polyurethane tube. In either case, openings of varying complexityare arranged along the microcable, for example, by plasma ablation, toform the electrically active areas 36, 38. To improve the electricalperformances, these areas may further be coated, for example by titaniumnitride.

These types of microcables are available, for example, from Fort WayneMetals Company Inc., Fort Wayne, USA, and heretofore have been used inthe medical field, notably for defibrillation conductors—but in adifferent arrangement of material. In these prior known applications,the structure is a multi-wire structure in which each strand includes acore of silver (to improve conductivity) coated with a stainless steelthickness. These microstructures, isolated or not, are then incorporatedinto a multi-lumen lead body, the construction of which is classic andwell known.

The benefits of the microcable structure described above lie in the factthat the less mechanically enduring elements (platinum-iridium orsilver) are encapsulated directly in (or are coated around) the nitinolsheath. The consequences of a possible fracture of the strands are thusminimized.

Alternatively, it is possible to have a strand of platinum-iridium inthe center of a 1×7-type multi-wire structure, the most fragile strandthen being the entwined by the most durable external strands.

Finally, platinum-iridium can be replaced by any radio-opaque materialsuch as tantalum, and nitinol can be replaced with materials having alower, but still suffiicent, endurance performance, or a less expensivematerial such as stainless steel MP35N, commonly used in the manufactureof standard conductors.

Insulating tubes 44 extending between electrodes 36, 38 are preferablytubes made of polyurethane (PU), glued on the microcable with a PU-typeglue. The fluidity of the glue, combined with the crevices formed by thetwist of the microcable, ensures an optimum link between the PU tube andthe microcable.

Platinum electrodes 36 and 38 are preferably crimped directly onto themicrocable. The small thickness of the electrode, combined with theductility of platinum, enhances the quality of the electrical contactwithout altering the microcable. On the other hand, the short length ofthe electrodes (e.g., 0.5 to 10 mm) significantly limits their impact onthe overall mechanical behaviour of the system, which is mostly dictatedby the microcable.

The individual surface of each electrode is about 0.5 mm², making itpossible to distribute a large number (e.g., up to twelve over a lengthof 1 to 200 mm in the longitudinal direction) without exceeding acombined total surface of 6 8 mm².

Due to the low cumulative active surface area, the advantages of a “highcurrent density” lead in terms of both physiological efficacy ofstimulation and lower energy consumption are provided, while at the sametime maximizing the chances of a physical, and thus electric, contact ofthe conductive surface (electrodes 36 and 38) of active portion 34 withthe excitable tissues, due to an increase in the number of electrodes.

Moreover, the alternation of conductive and insulating zones combinedwith the telescopic properties of the system allows for an improvedmanaging of the risk of phrenic stimulation. Indeed, if for a givenposition, the phrenic nerve is included in the electric field, it ispossible to slide the microcable in the lead body to position it in aremote area far from the phrenic nerve and thus to escape this parasitestimulation.

The configuration as described above allows separating the two problemsof placement of the lead in the coronary venous system and those relatedto the multiplication of the stimulation points. Indeed, the mechanicalfixing and maintaining of the lead is provided upstream by the lead bodyitself and by the retaining means 30, while the multiplication ofstimulation points is provided by the electrode array disposed along thetelescopic microcable, which allows stimulating a large area chosenindependently of the usual constraints of accessibility and stability.

In addition, to promote contact with the tissues, multiple types ofpre-formed shapes are possible for the distal end of microcable,including, without limitation:

-   -   A sequence of bends with variable radius in a same plane;    -   Sequence of bends with variable radius in a series of separate        planes;    -   Three-dimensional strongly curved trajectory, without any base        plane, for example, of the pigtail type,    -   the external dimensions of the pre-formed shape in the rest        state being included in a cube having a dimension of from 1 to        35 mm per side.

This particular configuration allows considering a particular variant ofthe implantation of the microcable alone (e.g., without a lead), itbeing then held in place by its very distal pre-formed shape.

In this embodiment, the placement in the vein is carried out byconventional catheter/sub-catheter means or brain access catheter.

FIG. 4 illustrates a second embodiment of an active part of the lead ofthe present invention. In this embodiment, the strand formed by thewires 46, 46′, 46″ of the microcable has applied on it an insulatingcoating of isolating PU adhesive 48, 48′, 48″, but on a smaller diameterthan the overall outside diameter of the strand so as to reveal, inreserve, conductive surfaces 50, 50′, 50″ (uncoated surfaces) of helicalshape. The active area of the active surface 34 is thus a triple helixshape 50, 50′, 50″ on the periphery of the microcable, on all or part ofthe length of the active region 34.

This solution makes it possible to “stretch” the surface in thelongitudinal direction of stimulation, without increasing the total areaof electrode.

With reference to FIG. 5, the graph shown of the polyurethane coatingdiameter (mm) against the exposed surface (mm²) illustrates the methodfor adjusting the total exposed surface (i.e., the active surface)according to the diameter of the coating of adhesive PU. The figures inthis chart are for a length of 40 mm for a three strand microcable ofoverall diameter 0.3 mm.

This variant makes it possible to further optimize the use of the activesurface of the electrode of the microcable, promoting its longitudinalextension. Note that the exhibited helical regions 50, 50′, 50″ may, ifdesired, occur only on some parts of the microcable, for example, byalternating active regions where the helical exposed surfaces areapparent and completely isolated regions, e.g. by means of PU tubes suchas the tubes 44 described with reference to the first embodimentdescribed above.

Furthermore, the bare conductive areas of the microcable may receive aporous coating, such as NiTi, or be coated with an additional layerformed by a carbon film deposited by sputtering, to improve thebiocompatibility properties between the microcable, its insulation andits environment, in order to avoid degradation of the parts in contactwith the blood flow. The U.S. Pat. No. 5,370,684 A and U.S. Pat. No.5,387,247 A, issued to Sorin Biomedica SpA, describe sputtering asubmicron thin carbon film, on implantable prostheses such as catheters,heart valves, etc., in polyurethane or in silicone. These documents areto be referred to for more details on the technology to make this carbonfilm deposit, which are incorporated herein by reference.

FIG. 6 shows a third embodiment of the present invention, which is avariant of the first embodiment, wherein the lead carries a plurality ofseparate microcables, each of which being similar to that describedabove and shown in FIGS. 2 and 3. In this embodiment, a single lead body24 is equipped with several internal parallel lumens from which aplurality of respective microcables laterally emerges.

Thus, in FIG. 6, the lead body comprises a plurality of sections 28 a,28 b, 28 c, each provided with an opening 32 a, 32 b, 32 c communicatingwith a respective lumen. It also includes at its distal end retainingmeans 30 and the hole 32 d.

Out of each of the holes 32 a, 32 b, 32 c, 32 d emerges a respectivemicrocable 34 a, 34 b, 34 c, 34 d, made according to either of theembodiments described above, for example, according to the firstembodiment in the example shown in FIG. 6. Each of these microcablesincludes its own network of electrodes 36, 38 electrically joinedtogether and separated by insulating parts 44, on the entire length ofthe emerging part.

This solution allows covering a large area of the left ventricle, with amultitude of electrodes connected in parallel, each branch correspondingto each active portion 34 a, 34 b, 34 c, 34 d remaining however,electrically independent thanks to its own electrical connection to theproximal end of the lead. This link allows connection to a correspondingterminal of a multi-connector head, for example, of the IS-4 type. Also,a multiplexing system may be included inside the lead to separatelyhandle connecting the different electrode arrays.

In general, whatever embodiment is employed, the technique justdescribed has many advantages, among which include, in particular:

-   -   simplified method of implantation, requiring only conventional        equipment;    -   stability of the electrical contact with the tissue regardless        of the size of the vein;    -   possibility of extending the usable portion of the vein,        including the distal area to the venous system, with an        excellent adaptation to the thin venous networks, while        maintaining an attachment point in the target vein (at the        retaining means 30);    -   effective distribution of the electrical flow in the deep        regions of the epicardium;    -   high reliability as a result of the mechanical performances of        the nitinol structure of the microcable;    -   overall mechanical simplicity, therefore having a low        manufacturing cost and high reliability;    -   radiopacity, based on the platinum core of each strand forming        the microcable as well the platinum rings (in the case of the        first embodiment);    -   Easy extraction, thanks to (i) the isodiametric profile of the        microcable, (i) its small diameter, and (iii) to its high        tensile strength (one-piece robust structure of the microcable        at its end); for the lead body, it is sufficient to simply        unscrew the distal end of the lead body at the level of        retaining means 30 before removing the lead body.

One skilled in the art will appreciate that the present invention can bepracticed by other than the embodiments described herein, which areprovided for purposes of illustration and not of limitation.

1. A pacing lead for implantation in a coronary vein system (14-22) forthe stimulation of a left cavity of the heart, comprising: a telescopicmicrocable (42) made of a conductive material having a distal end and aproximal end, said distal end having an active free part (34) comprisinga plurality of distinct bare areas (36, 38, 50, 50′, 50″), wherein saiddistinct bare areas form a network of stimulation electrodeselectrically connected together for contact (40) with a wall of a targetvein (22) of the coronary system, and said proximal end having aterminal for coupling said microcable to a generator of activeimplantable medical device, wherein said telescopic microcable (42)comprises a diameter selected from between 0.5 and 2 French, a pluralityof strands twisted together, in which at least some strands incorporateeither a core of a radiopaque material wrapped by a sheath of amechanically durable material, or vice versa.
 2. The lead of claim 1,wherein the distal end of the microcable comprises a pre-formed shapehaving at least two dimensions.
 3. The lead of claim 2, wherein theexternal dimensions of the pre-formed shape in a rest state are includedin a cube having a dimension of from 1 to 90 mm per side.
 4. The lead ofclaim 1, further comprising a lead body comprising a hollow sheath (26,28) made of a deformable material and with a central lumen open at bothends, wherein the microcable is slidably disposed in and spans theentire length of the lead body and is extendable beyond the distal end(32) thereof, the portion of microcable emerging beyond the distal endof the lead body forming said active free part (34).
 5. The lead ofclaim 4, wherein the distal end of the lead body comprises a firstdiameter and a means for retaining said lead body in said coronary veinsystem (30) comprises at least one relief formed on the lead body andlocally presenting a second diameter greater than the first diameter. 6.The lead of claim 5, in which the relief further comprises a helicalrelief having a thread wrapping at least part way around the lead body.7. The lead of claim 5, wherein the second diameter is less than orequal to 7 French.
 8. The lead of claim 4, wherein the lead bodycomprises a main portion having a first diameter (26) distally extendedby a transition part (28) having a second diameter smaller than that ofthe first diameter.
 9. The lead of claim 8, wherein the first diameteris less than or equal to 6 French, and the second diameter is less thanor equal to 5 French.
 10. The lead of claim 4, wherein the lead bodyfurther comprises : a common lead body (28 a, 28 b, 28 c) having aplurality of distinct telescopic microcables housed in the lead body andsliding therein, each said microcable having an active free part, andthe respective active free parts (34 a, 34 b, 34 c, 34 d) of thedifferent microcables emerging from the lead body in separate locations(32 a, 32 b, 32 c, 32 d) longitudinally spaced along the lead body. 11.The lead of claim 1, wherein the plurality of distinct bare region(s) ofthe active free part of the microcable comprises an exposed totalsurface area of at least 1 mm².
 12. The lead of claim 11 wherein saidexposed total surface area is from between 4 and 6 mm².
 13. The lead ofclaim 1, wherein the microcable active free part comprises a lengthadjustable between 1 and 200 mm.
 14. The lead of claim 1, wherein theplurality of distinct bare regions (36, 38) extend in succession alongthe active free part.
 15. The lead of claim 14, wherein the distinctbare areas (36, 38) are separated from each other by portions of a tube(44) made of an electrically non-conductive material, wrapping andsheathing the microcable between two consecutive bare areas.
 16. Thelead of claim 14, wherein the distinct bare regions bear tubular ringsmade of an electrically conductive material, crimped on the microcable.17. The lead of claim 16, wherein the electrically conductive materialof the tubular rings crimped on the microcable is a radiopaque material.18. The lead of claim 14, wherein the microcable comprises a multi-wirestructure coated with an insulating material, in which the distinct bareareas are formed by ablation of the insulating material along themicrocable.
 19. The lead of claim 18, comprising a deposit of nitridetitanium on the distinct bare areas.
 20. The lead of claim 14, whereineach distinct bare area has a length in the longitudinal direction ofbetween 0.5 to 10 mm.
 21. The lead of claim 1, wherein the active freepart of the microcable comprises at least one bare helical area (50,50′, 50″) extending along the active free part.
 22. The lead of claim21, wherein the microcable has on at least a portion of the active freepart, a strand formed of a plurality of twisted strands (46, 46′, 46″)having a corresponding plurality of bare helical regions (50, 50′, 50″),isolated from each other in the circumferential direction by helicalcoatings (48, 48′, 48″) of electrically non-conductive material.
 23. Thelead of claim 1, wherein the radio-opaque material comprises platinumiridium.
 24. The lead of claim 1, wherein the mechanically durablematerial comprises NiTi.
 25. The lead of claim 1, wherein themechanically durable material comprises stainless steel.